1. Field of the Invention
The present invention relates to the use of hydroxyalkylacrylate containing copolymers dissolved in organic liquids to produce compositions which are effective defoamers for use in pulp and paper mill operations, particularly for use in brown stock washers.
2. Description of the Prior Art
The problem of foam control in pulp and paper mill operations is a continuing one. Generally, it has been most effectively dealt with by using various petroleum oil-based compositions containing an alkylene diamide and/or hydrophobic silica (silicone coated silica). Oil-based amide defoamers contain a minimum of two ingredients: a wax with a high melting point (usually a fatty diamide) dispersed in a petroleum hydrocarbon oil carrier. The most commonly used diamide is ethylenebis(stearamide), but other diamides or mixtures of diamides can also be found in defoamer blends. Typically, the weight fraction of diamide is between 2 and 8% whereas the weight fraction of the petroleum oil is well over 80%. The oil carrier varies in composition from one defoamer to another but generally consists of a low viscosity mineral oil with paraffinic or cycloparaffinic hydrocarbons. In addition to the diamides and petroleum oil, the blends may also contain other agents such as hydrophobic silica and silicone oil, various emulsifiers and stabilizers, but these constituents generally comprise less than 10% of the formulation.
While these diamide-based compositions are effective defoamers for brown stock washers in pulp mills, they have recently been suspected of contributing to deposition problems in various locations in the mills. (Dorris et al. "Analysis of Amide Defoamers in Kraft Mill Pitch Deposits," J.Pulp & Paper Science, 11:5, J149-J154, September 1985) And recently there has been evidence that the petroleum oil in this type of defoamer is an indirect source of the 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) produced in kraft bleach plants. (Allen et al. manuscript distributed at the 8th International Symposium on Chlorinated Dioxins and Related Compounds, Umes, Sweden, Aug. 21-26, 1988) In addition, they have not been found useful on paper machines because they are not able to completely disperse in water and thus they have been found to cause deposits and/or oil spots on the paper produced. Also, diamides are considered a primary source of pitch deposit build-up which is a major problem.
Alternative petroleum oil-based defoamers have been prepared from a wide variety of chemicals. For example, U.S. Pat. Nos. 3,751,373 and 3,935,121 disclose defoamers based upon a combination of a fatty acid or alcohol, a polyethylene glycol mono- or di- ester of a fatty acid, a petroleum sulfonic acid, and 65-98% organic liquid. One example of a commercial aqueous defoamer is an aqueous emulsion of fatty alcohols --although it does not contain any petroleum oil phase, it does contain high melting waxes which are known to interfere with certain later processing steps. These defoamers are generally not as effective as those containing EBS and its homologues, but also do not cause the spotting problem on paper machines.
Therefore there is a need for an effective defoamer which does not contain EBS and/or other diamides, and preferably does not contain any petroleum oil. Accordingly, it is an object of the present invention to produce such defoamer compositions and to utilize them on brown stock washers and in other paper-making operations.